Combinations of materials to minimize ESR and maximize ESR stability of surface mount valve-metal capacitors after exposure to heat and/or humidity

ABSTRACT

Single element and/or multiple element valve-metal, solid-electrolyte, surface-mount capacitors are manufactured using one or more materials taken from the following three categories of materials: graphitic carbon, highly-conductive metal-powder-filled paint, and metallic terminals. The resulting capacitors have lower equivalent series resistance (ESR) at 100 kHz than do similar capacitors manufactured with conventional materials and with conventional techniques. Moreover, not only do these devices possess lower “as-manufactured” ESR, but also their ESR is substantially more stable (less increase in ESR) when these devices are exposed to IR reflow temperatures, high humidity, thermal shock, 1000 hours at 150° C., and 1000 hours at 175° C.

FIELD OF THE INVENTION

The invention relates to combinations of materials (graphitic carbon,highly-conductive metal-powder-filled paint, and metallic terminals) andmethods of using these materials to manufacture solid-electrolyte,surface mount valve-metal capacitors having exceptionally low ESR(equivalent series resistance) and high ESR stability after exposure toextreme heat and/or humidity.

BACKGROUND OF THE INVENTION

All electronic circuits contain capacitors. These devices store anddispense electrical charge in response to circuit currents, resulting inpredictable increases and decreases of voltage across their terminals.It is this predictable and limited short-term variation of terminalvoltage that makes capacitors useful as coupling and filtering devicesin electronic circuits. Specifically, capacitors are useful in circuitlocations where one does not want the voltage to change rapidly. Oneexcellent use of capacitors is to minimize or “filter-out” both randomand periodic fluctuations from the output stage of direct-current (DC)power supplies.

The ability of capacitors to perform their filtering function is limitedby the unwanted “parasitic” resistances that result from the use ofreal-world, non-ideal materials in their construction. These parasiticresistances, collectively known as the finished capacitor's equivalentseries resistance (ESR), manifest themselves in the user's electricalcircuit as though they were a discrete resistor connected in series withthe capacitance of the capacitor. Whereas ideal capacitor elementsinherently oppose rapid voltage shifts in the face of changing current,the voltage across resistors changes instantaneously and proportionallyto changing current. So if a practical capacitor has significant ESR,the resulting instantaneous voltage shifts across the capacitor's ESR,that are proportional to changes in circuit current, undermine thevoltage-stabilizing influence of the capacitor. If the ESR becomes toolarge, the capacitor becomes useless as a filtering device.

Early electronic circuits designed with vacuum tubes typically employedhigh voltages and relatively low currents. This was a consequence of thehigh impedance (ratio of voltage to current) of these early electronicdevices. Capacitors used in power supply filter applications typicallyfiltered high voltages (>100 V), experienced low fluctuating currents(ripple current<1 A), and rarely experienced significant ripple currentat frequencies greater than 120 hertz (cycles per second). Routinemanufacturing methods and materials yielded filter capacitors with lowenough ESR to easily satisfy the needs of these early electroniccircuits.

Change has come to the world of electronics in several forms, one ofwhich is change in the kinds of active devices employed in circuits.Vacuum tubes were replaced by discrete transistors and, now, discretetransistors have largely been displaced by integrated circuits. Evenintegrated circuits have evolved steadily. An example is microprocessorswhere the number of active devices (transistors) in a state-of-the-artmicroprocessor chip doubles every year or so. The most significantimpact of this evolutionary change is that power supply voltages havefallen steadily (to limit power consumption in the circuits) and supplycurrents have risen (reflecting the greater number of active devices inintegrated circuits and the higher frequencies at which these devicesoperate).

Since circuit voltages are now lower and currents higher, the ESR ofcapacitors has become of critical interest to the engineers who designthese modern circuits. In contrast to the days when if a capacitor'scapacitance were high enough to meet the circuits needs then it's ESRwould almost certainly be low enough, today's circuits demand such lowESR that engineers frequently must use more capacitance than wasformally required in order to obtain sufficiently low ESR for propercircuit operation. This leads to circuits that are physically larger andmore expensive than is necessary. There is a distinct need for capacitormanufacturers to supply capacitors whose ESR is low enough to meetcircuit requirements without the need to employ excessive capacitance(and occupy unnecessary circuit volume).

Another change in the world of electronics is the shift frompoint-to-point wiring to the use of printed circuits, and the subsequentshift from the use of leaded components on printed circuit boards to theuse of surface-mounted components. These changes have provided marvelousimprovements in circuit compactness and manufacturing productivity, buthave had significant impact on the physical requirements of electroniccomponents. In the case of point-to-point wiring, if a component weresensitive to soldering heat, a discrete heat-sink could be attached tothe component's leadwire between the point of soldering and the body ofthe component to minimize component heating during the solderingprocess.

In the case of circuit boards used with leaded components, the leadswere inserted through holes in the board and were subsequently solderedon the opposite side. This arrangement reduced the practicality of heatsinking during soldering. But at least the heat was applied on the sideof the board opposite from that of the component, thus limitingcomponent heating to that caused by heat conduction through theleadwires.

Today, almost all components are mounted to the surface of circuitboards by means of infra-red (IR) or convection heating of both theboard and the components to temperatures sufficient to reflow the solderpaste applied between copper pads on the circuit board and thesolderable terminations of the surface mount technology (SMT)components. Not only is heat-sinking impractical in this case, it wouldactually defeat the effectiveness of the soldering method. A consequenceof surface-mount technology is that each SMT component on the circuitboard is exposed to soldering temperatures that commonly dwell above180° C. for close to a minute, typically exceed 230° C., and often peakabove 250° C. If the materials used in the construction of capacitorsare vulnerable to such high temperatures, it is not unusual to seesignificant positive shifts in ESR which lead to negative shifts incircuit performance. SMT reflow soldering is a significant driving forcebehind the need for capacitors having temperature-stable ESR.

Another driving force behind the need to manufacture capacitors havingtemperature-stable ESR is high circuit temperatures. As circuits areminiaturized, it becomes more difficult to remove the heat that isgenerated by normal circuit operation. Thus, it is not unusual forcapacitors to operate in high ambient temperature environments (up to125° C.). Also, electronics are becoming an integral part of automotiveapplications, especially in under-the-hood applications. It is notunusual for the ambient environment to reach 150° C. in suchapplications with the desire to go to 175° C. and potentially higher.Another issue with automotive applications is temperature cycling andthermal shock. It is essential that ESR remain stable in the face ofboth high temperature and high rates of change of temperature.

A final threat faced by capacitors is humidity. Some high-reliabilitycircuits are cleaned after the SMT mounting process to removecontaminants (flux residues and other contaminants). Freon-basedsolvents were used in the past with a high degree of cleaningeffectiveness and minimal impact on component reliability. Today, withconcern about the use of potentially ozone-depleting substances, manyelectronics manufacturers are using cleaning systems that arewater-based.

Typical cleaning cycles can last for more than an hour and componentscan be exposed to significant heat and humidity which can cause moistureto permeate through the component's case, potentially saturating thedevice. Also, since much manufacturing is done in the “Pacific-Rim”countries, it is not unusual for components to be exposed to significantheat and humidity if they are stored for significant time innon-air-conditioned warehouses. Moisture can degrade ESR by attackingthe integrity of electrical connections within the capacitor with acombination of oxidation and corrosion. It has become essential thatcapacitors resist unwanted positive shifts in ESR when they are exposedto high-humidity environments.

Production of low-ESR capacitors has proven to be a formidablechallenge. Capacitors manufactured with traditional materials andmethods have excessively high initial ESR. Moreover, after thesecapacitors are exposed to SMT reflow temperatures by the user, the ESRtends to shift upward still more. After reflow mounting, exposure tohumidity, high operating temperatures, and/or thermal shock results infurther, steady deterioration of ESR which can ultimately lead to thefailure of the device to perform adequately in the circuit.

A particular capacitor that is desirably optimized for low ESR is avalve-metal, solid-electrolyte, surface-mount electrolytic capacitor.Such capacitors have as their dielectric thin, highly insulating anodicoxide film which may be produced electrolytically on the so-called valvemetals (e.g. tantalum, aluminum, titanium, and niobium). The positiveterminal of the finished capacitor is connected to the non-oxidizedportion of the valve metal which supports the metal-oxide dielectriclayer. The negative terminal is connected to the outermost layer of asuccession of conductive layers which are formed on the exposed surfaceof the dielectric layer. A typical valve-metal capacitor comprises oneor more metal-oxide capacitor elements which are connected electricallyto metallic terminals and which are encapsulated in a protective plasticcovering, coating, or case.

It is desirable to produce valve-metal, solid-electrolyte, surface mountelectrolytic capacitors having low ESR. It is also desirable to producecapacitors that are substantially unaffected by heat from SMT reflowsoldering, humidity exposure at elevated temperature, aggressive thermalshock conditions, and continuous operational exposure to hightemperatures.

SUMMARY OF THE INVENTION

It is an objective of the invention to create a valve-metal,solid-electrolyte, surface mount electrolytic capacitor havingexceptionally low equivalent series resistance (ESR).

Another objective of the invention is to create a valve-metal,solid-electrolyte, surface mount capacitor whose ESR is substantiallystable after the cumulative environmental stress created by IR reflowsoldering, humidity exposure at elevated temperature, thermal shocktemperature cycling, and continuous operational exposure to various hightemperatures (e.g. 1000 hours at 150° C. and 1000 hours at 175° C.).

Consistent with these objectives, the invention is directed to thecombination of specific materials from three categories of materialsused in the construction of valve-metal, solid-electrolyte, surfacemount electrolytic capacitors. These three categories of materials aregraphitic carbon, highly-conductive metal-powder-filled paint, andmetallic terminals.

When the materials of the present invention are selected and applied asdescribed, the result is a valve-metal, solid-electrolyte, surface mountelectrolytic capacitor having extraordinarily low ESR and also havingESR that is substantially more stable than that of prior art deviceswhen the capacitors are exposed to the cumulative environmental stressof multiple IR reflow profiles, intense humidity at high temperature,multiple thermal shock cycles, and/or continuous operational exposure tohigh temperatures.

The invention relates to the use of various combinations of (1) ahigh-purity, micro-graphited suspension of carbon particles for thecarbon layer, having a thermally stable binder or a binder thatdecomposes to conducting species, (2) high metal content paint for themetal paint layer, and (3) high electrical conductivity metal alloy forthe metallic terminal having selectively plated surfs to enhanceinterfacial conductivity and interfacial electrical stability betweenthe lead frame, the metal paint, and the conductive, silver-filledadhesive (or similar material) that joins them.

The invention is directed to a valve metal capacitor comprising at leastone anodized element having a dielectric layer formed on the element, aconductive layer formed on the dielectric layer, a graphitic carbonlayer formed on the conductive layer, a metal-powder-filled paint layerformed on the graphitic carbon layer, and a negative metallic terminalattached to the paint layer. At least one of 1) the graphitic carbonlayer is formed from graphitic carbon having at least 73% graphitecarbon in a binder stable at temperatures of at least 150° C. or abinder that decomposes into conducting species when exposed to reflowtemperatures; 2) the metal-powder-filled paint layer has a resistivityof less than about 0.0005 Ω·cm and comprises metal powder in a binderstable at temperatures of at least 200° C.; or 3) the negative metallicterminal has a conductivity of at least 90% the conductivity of purecopper, wherein at least the surface of the negative metallic terminalconnected to the metal-powder-filled paint layer is plated with aprotective coating to prevent oxidation of the negative metallicterminal, and wherein the protective coating is thermally stable attemperatures of at least 200° C.

The interaction of at least two of the materials of the inventionprovides unexpected improvement in ESR stability, more so than one wouldpredict based on his knowledge of these material's impact on“as-manufactured” ESR when used alone. This synergistic effect among thematerials was hitherto unknown and unanticipated by prior art practice.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an electrical schematic diagram of the circuit model thatdescribes the electrical impact on device ESR of the materials used inthe manufacture of valve-metal, solid-electrolyte, surface mountcapacitors that contain six (6) capacitor elements.

FIG. 2 is an example of a multi-element capacitor that behaves accordingto the electrical diagram of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is particularly directed to the preparation ofultra-low ESR anodized valve metal, powder-metallurgy surface mountelectrolytic capacitors, e.g. 1000 μF, 4V, MnO₂ capacitors with ESR nomore than 10 mΩ; 680 μF, 6V, MnO₂ capacitors with ESR no more than 12mΩ; and 470 μF, 10V, MnO₂ capacitors with ESR no more than 15 mΩ. Thevalve metal may be any suitable valve metal including tantalum,aluminum, niobium, or titanium. A dielectric layer is formed on thevalve metal.

A conductive layer is formed on the dielectric layer to provide thenegative connection to the dielectric layer. The conductive layer iscreated by impregnating the anodized element with manganese dioxide, aconductive polymer, a meltable conductive salt, or other suitable meanswithin the skill of the art.

The conductive layer is then covered with a layer of graphitic carbonand then with a layer of highly-conductive metal-powder-filled paint.The carbon layer acts as a buffer layer between the conductive layercovering the dielectric and the metal in the highly-conductivemetal-powder-filled paint, minimizing chemically driven increases ininterfacial resistance that occur in the absence of the carbon.

The metal paint covered portion of the capacitor element is thenelectrically connected to the negative metallic terminal of the finishedcapacitor by means of conductive, metal-filled epoxy adhesive or othersimilar means. Finally, the now fully-assembled device is encapsulatedwithin a suitable container which has provisions for electricalconnections between the capacitor element(s) and the external electricalcircuit.

At least one, preferably two, and most preferably all three of thefollowing stability-promoting materials are used in the preparation ofthe capacitor: 1) the graphitic carbon layer is formed from graphiticcarbon having at least 73% graphite carbon in a binder stable attemperatures of at least 150° C. or a binder that decomposes intoconducting species when exposed to reflow temperatures. 2) themetal-powder-filled paint layer has a resistivity of less than about0.0005 Ω·cm and comprises metal powder in a binder stable attemperatures of at least 200° C. 3) the negative metallic terminal has aconductivity of at least 90% the conductivity of pure copper, wherein atleast the surface of the negative metallic terminal connected to themetal-powder-filled paint layer is plated with a protective coating toprevent oxidation of the negative metallic terminal, and wherein theprotective coating is thermally stable at temperatures of at least 200°C.

The combinations of materials of the invention not only reduce ESR, butalso stabilize ESR in the face of exposure to severe environmentalstress more than could be predicted from the “as-manufactured”performance alone. After exposure to extreme environmental stress, theESR of capacitors made with the inventive combinations of materials islower than the ESR of capacitors made with conventional combinations ofmaterials—by an amount greater than is seen before exposure to thisenvironmental stress.

Another way to lower the ESR of such capacitors is to alter theirinternal structure so that electrical path lengths are minimized and theeffective surface area of the capacitor element(s) inside is maximized.Piper (3,686,535) discovered that subdividing one large capacitorelement into several smaller elements, and connecting these smallerelements electrically in parallel yields capacitors that have lowerimpedance and, thus, lower ESR when they are compared to capacitors madewith one large capacitor element of similar capacitance and ratedvoltage.

A preferred embodiment thereof combines the inventive combinations withPiper's multi-element design to achieve capacitors with extraordinarilylow ESR. The invention works well with both single-element, valve-metal,solid-electrolyte, surface mount capacitor designs, and multi-elementcapacitors with at least two, preferably at least four capacitorelements per device.

An electrical schematic diagram of a six-element, valve-metal,solid-electrolyte, surface mount capacitor appears in FIG. 1. Thediagram identifies discrete resistances that result from the materialsused to construct the individual capacitor elements, the resistancesinvolved in the electrically-parallel interconnection of the elements,and the resistances of the metallic terminals that are used to connectthe parallel elements to an external circuit. The resistances that arepertinent to the invention are identified as “C: Carbon LayerResistance,” “P: Silver Paint Layer Resistance,” “I: InterfacialResistance,” and “T: Metallic Terminal Resistance.”

The Graphitic Carbon Layer

The graphitic carbon layer may be prepared by dipping a capacitorelement into a suspension of highly graphitized carbon particles andbinder, and then drying/curing the carbon layer that remains on thesurface of the element after the element is withdrawn from thesuspension. Prior to curing, the layer should be sufficiently dried tosubstantially remove solvents or water that might volatilize and therebygenerate localized pressure gradients which can cause delaminations orother physical or electrical disruptions of the finished carbon layer.

The high degree of graphitization enhances the bulk conductivity. A highdegree of graphitization means at least 73%, preferably at least 75%graphitic carbon (versus amorphous carbon). Preferably, the percentsolids of the suspension of graphitized carbon particles is maintainedbetween about 2% and about 15%, preferably between about 5% and about100%, by weight.

The pH is generally between 8 and 11, preferably between about 9 andabout 10 to maintain chemical stability. The pH may be adjusted by theaddition of an appropriate base such as ammonia or a volatile amine. Thegraphitized suspension may also be stabilized and purified bycirculation in a dipping tank, filtering to remove clumps of carbon,high-shear mixing, and/or ultrasonic treatment to re-suspend clumps.

The carbon layer is applied (including the drying and/or curing process)so that there is intimate electrical contact between the carbon layerand the two adjacent layers that the carbon layer separates. Thisintimate contact achieves enhanced interfacial conductivity from eachlayer to the next. The degree of graphitization also improves theconductivity of the interfacial junction. The highly graphitized carbonsuspension must be stable to avoid clumping which leads to non-uniformcoverage and poor contact.

The binder material in which the deposited graphitic carbon is suspendedmust be either a material which is stable when exposed to elevatedtemperatures (above about 150° C.), or a material that decomposes toconductive, carbonaceous byproducts rather than low-conductivity organiccompounds after exposure to such elevated temperatures. Suitable bindermaterials include starch, solubilized cellulose, and organic materialsthat give rise to carbon instead of boiling away.

The thickness of the carbon layer is preferably about 0.0001 inches toabout 0.003 inches, more preferably about 0.0005 inches to about 0.002inches. The carbon layer must be thin not only to reduce the resultingseries resistance, but also to enhance the mechanical strength of thecarbon layer. The bulk strength of graphitic carbon is not inherentlyhigh. However, since thin layers conform better to the irregularsurfaces present in valve-metal, solid-electrolyte capacitors, theyallow for subsequent stronger layers of materials (e.g. thermo-set epoxybased silver paint) to take on the same irregular surface shape, thusinterlocking with the irregular surface and boosting the effectivestrength of the carbon layer.

Thicker layers of graphitic carbon cause higher ESR because resistanceis proportional to the layer's thickness and also cause unstable ESRbecause thick layers have less mechanical strength than thin layers, asdiscussed above. Reduced mechanical strength can lead to mechanicalseparations in the carbon layer after finished capacitors are exposed toenvironmental stress, causing higher ESR. Thicker carbon layers are alsomore difficult to dry/cure. If the drying/curing process is inadequate,subsequent application of high heat can cause trapped solvents ormoisture to evaporate and generate high localized pressure. Thispressure can damage the integrity of the carbon layer, thus raising theESR of the finished capacitor. The drying/curing process is carried outso as to facilitate the evaporation of the solvent without boiling,typically by air drying prior to oven drying/curing.

However, the layer of graphitic carbon must be thick enough to provide achemical buffer between the two materials it separates. Also, since thinlayers of graphitic carbon result from dipping into very dilutesuspensions which aggressively wick into porous structures, it ispossible for the carbon to migrate deep into the structure. Thegraphitic carbon should effectively coat the surface of the material,not permeate it.

A suitable micro-graphited carbon suspension is DAG1050, manufactured byAcheson Colloids Company.

The Metal-Powder-Filled Paint Layer

The carbon coated capacitor element is then dipped into a highlyconductive metal-powder-filled paint. The highly-conductivemetal-powder-filled paint preferably has an organic content whichcomprises thermally stable cross-linked thermoset epoxy or polyimidewith low post-cure ionic content. Highly conductive means bulkresistivity less than about 0.0005 Ω·cm. Thermally stable means that thebinder is stable at a temperature of at least 200° C. and preferablybetween 200° C. and 300° C. for periods longer than 10 minutes. Also,the metal-powder-filled paint is indefinitely stable to decomposition at150° C., preferably at least 175° C. (for at least 1000 hours). A lowpost-cure ionic content means 100 ppm or lower ionic material based onweight of dried paint.

The conductive metal paint layer may be applied by dipping the capacitorelement into a pool of paint, widrawing it at a controlled rate, anddrying/curing the layer so produced. Suitable metal powders includesilver, gold, nickel, or copper. Preferably the metal powder is silver.The powder may be in any suitable form such as particles or flakes.

The metal powders are in a suitable thermally stable binder such asthermosetting epoxy, thermosetting polyimide, silicone epoxy or phenolicresins. The binder may be thinned with a suitable solvent such aspropylene glycol mono methyl ether acetate (PMA), butyl acetate (BA),dipropylene glycol mono methyl ether (DMM), and dimethyl esters ofsuccinic, glutaric, and/or adipic acids sold by DuPont under the tradename DBE.

The metal paint layer provides an intimate, low-resistance connection tothe graphitic carbon and provides a highly conductive surface which cansubsequently be bonded to the negative terminal (or leadwire) of thefinished capacitor by means of conductive silver adhesive, solder, orsimilar material. The metal paint also provides an approximatelyequipotential (electronically) surface that effectively captureselectrical displacement currents generated within the capacitor so thatthey can be guided to the negative terminal with a minimum ofunnecessary electrical resistance. Thus, it is critical that the metalpaint layer have low bulk resistivity after drying/curing and be appliedover as much of the surface of the capacitor element as is practical.Low bulk resistivity means less than about 0.0005 Ω·cm.

The metal paint layer is preferably dried prior to curing to avoidgeneration of localized pressure in the metal paint coat, thus leadingto ruptures, delaminations, or other physical disruptions that raisecapacitor ESR.

After drying/cuing, the paint preferably has at least about 80% metalsolids by weight based on total weight of the paint, more preferablygreater than about 85% and most preferably greater than about 90%, inorder to achieve acceptable conductivity. The metal flake used in thepaint must have appropriate surface morphology to insure adequateflake-to-flake contact, flake-to-flake contact, and exposure of surfaceflake edges after the paint has dried/cured. These favorable silverpaint properties are also influenced by the shrink rate of the bindermaterial.

Lubricants used during the milling of the flake must be chosen to becompatible with the binder materials of the paint to maximize electricalconductivity after drying/curing. Finally, the paint's viscosity ispreferably controlled by the addition of a suitable solvent/thinner inorder to optimize the thickness and uniformity of the resulting coat.

The binder of the metal paint must not interfere with the electricalconductivity of the dried/cured paint or its electrical stability whenexposed to environmental stress. The binder must be thermally stable soas to not deteriorate upon exposure to solder reflow temperatures whichcan exceed 250° C. This stability can be achieved either by employingonly materials stable at reflow temperatures or by insuring that anynon-thermally stable materials are decomposed and removed during thecuring/drying process while the resulting controlled shrinkage bringsthe silver flakes into mutual contact. The highly-conductivemetal-powder-paint should withstand IR reflow temperatures (typicallybetween 175° C. and 260° C.) for brief periods (less than 3 hours) orsomewhat lower temperatures (typically between 125° C. and 175° C.) forextended periods (up to 1000 hours, or more) without substantialincrease in the ESR of the capacitor. Materials that can successfullysurvive solder reflow temperatures include, but are not limited to,thermosetting cross-linked epoxy resins, phenolic resins, and/orpolyimides.

The metal paint should be electrically stable when exposed to highhumidity. Thus, the ionic content of the binder is minimized to preventcorrosion of the metal flake in the presence of humidity. That is, thepaint is substantially free from mobile ionic species. Also, the bindershould adequately coat the metal flakes, resist absorption of moisture,and be mechanically stable in the presence of moisture (not swell).

A suitable metal paint is DP5262, a silver paint manufactured by duPont.Preferably the silver paint contains more than 80% silver content byweight after curing and is thinned with either propylene glycol monomethyl ether acetate, butyl acetate, dipropylene glycol mono methylether, or one or more dibasic esters sold by duPont under the brandnameof “DBE.” The silver paint provides a suitable low-resistance,equipotential silver coat that can be joined effectively to thecapacitor's negative terminal and demonstrates the desired electricaland mechanical stability when exposed to IR reflow temperatures and/orhigh humidity.

The metal paint preferably covers between 50% and 95% of the externalsurface area of the capacitor element so as to maximize theequipotential conductive surface that collects the displacement currentsgenerated while charging and discharging the capacitor element.

The Metallic Terminals

The metallic terminals contain any suitable metal such as copper,silver, or an alloy having at least 90% conductivity of pure copper suchas Alloy 194. Such alloys may be “half-hard,” “hard,” “extra-hard,”“spring-hard,” or “extra-spring-hard.”

The metallic terminals are preferably predominantly copper which isselectively plated to minimize heat- and humidity-driven increases inresistance caused by oxidation, corrosion, and/or growth ofintermetallic species.

The metallic terminals are preferably a thin sheet of electricallyconductive metal that is either punched or etched to obtain a pattern ofconductive metallic regions to which the positive and negative terminalsof the capacitor element(s) are either welded, soldered, or attached bymeans of conductive silver adhesive, for example. After this assemblyprocess, the multiple assembled capacitors can be handled in mass on thelead frame to simplify the process of conformal coating, to facilitateautomated processing during almost all assembly steps, and electricaltest and measurement. Then each finished capacitor is separated from itsneighbors on the lead frame and the remaining, protruding strips of leadframe metal are folded around the leading and trailing edges of thefinished capacitors in order to provide easily solderable positive andnegative terminals for the finished capacitors.

Alternatively, metallic terminals can be formed into the shape ofendcaps which cover the positive and negative ends of one or morecapacitor elements that have been conformally coated with anelectrically insulating encapsulant leaving a portion of each metalpaint coated capacitor element's body uncovered, via masking, to provideelectrical connection to the negative metallic terminal. Such methodsare well known to those skilled in the art and include fluidized bed andliquid immersion. The negative metallic terminal (cathode) connection isachieved by attaching, by means of conductive metal-filled adhesive, thesingle negative end cap to the exposed portion of the metal paint whichcoats the negative terminal(s) of the capacitor element(s). The positivemetallic terminal (anode) connection is achieved by welding the positivesingle end cap to the riser wire(s) of the capacitor element(s).

Suitable adhesives include silver-filled conductive adhesives,gold-filled conductive adhesives, and nickel-filled conductiveadhesives.

To form the ultra low-ESR capacitors, the alloy from which the metallicterminal is constructed must have low electrical resistivity (at least90% of the conductivity of copper). The terminal metal must also presentan easily soldered surface during the customer's IR reflow mountingprocess. There must be successful solderability after exposure to heatand humidity which tend to oxidize and/or corrode metallic surfaces. Thesolderability characteristic is usually provided by solder-plating themetallic terminal. Occasionally, capacitors are mounted to circuits bymeans of conductive, metal-filled epoxy. In this case, the externalsurface of the metallic terminal must also be protected from oxidationand/or corrosion, but the protective coating is usually not solder. Theterminal metal must generally be soft enough to allow bending of thepositive and negative terminals into position or forming end capswithout generating stress fractures, but also be tough enough tomaintain its physical shape during the various manufacturing steps.

Generally, valve-metal, solid-electrolyte, electrolytic capacitorelements are connected to the positive metallic terminal by resistancewelding. That is, the positive terminal of the capacitor element ispressed against the terminal metal by pressure exerted by a pair ofconductive electrodes. A sort burst of current is directed through thevarious metals and enough heat is generated in the terminal metal andpositive terminal of the capacitor element to cause them to weldtogether (fuse), with minimal fusing to the electrodes of the welder.High electrical conductivity in the metallic terminal does not usuallyprovide successful resistance welding because it is difficult to isolatethe resulting heat to only the welded junction, a situation whichfrequently results in either melting of the welding electrodes, stickingbetween the metallic terminal and an electrode, sticking between thepositive terminal of the capacitor element and an electrode, or allthree. These problems generally result in poor weld strength and/or weldreliability. For this reason, most conventional metallic terminal alloysdo not possess superior electrical conductivity, many having ten times(or more) the electrical resistivity of superior alloys. Thus,electrical conductivity is frequently traded off to achieve acceptableweld strength. However, electrode metals and welding schedules may bechosen that are compatible with high-conductivity metallic terminalalloys. Also, these connections can be made by laser welding orultrasonic joining techniques.

The interface between the metallic terminal and the joining material(silver-filled adhesive, solder, etc.) used to connect the metal paint(negative terminal) of the capacitor element to the metallic terminalmust be electrically stable not only during the manufacturing process,but also during exposure to environmental stress. If the metallicterminal's surface is prone to oxidation or corrosion, it may bedifficult to create an acceptable electrical connection during themanufacturing process, but it will almost certainly be difficult tomaintain a stable electrical connection during exposure to environmentalstress.

One common solution is to coat the entire metallic terminal with thesame solder plating that is employed to keep the terminals of thefinished capacitor solderable. There are difficulties with thisapproach. One difficulty is that the solder plating tends to melt duringexposure to IR reflow conditions, and the molten solder can be forcedoutside of the encapsulating material. Another problem with solderplating is that intermetallic species can form under the solder coating.During IR reflow, the solder melts, but then is unable to wet to theintermetallic species upon which it rests. Upon resolidification, thesolder no longer makes adequate electrical connection between thejoining material discussed above and the base-metal of the metallicterminal. Another problem is that the molten solder can scavenge thesilver from conductive silver adhesive by dissolving it. These problemscause the electrical resistance of the junction to rise after IR reflowexposure, which raises the ESR of the capacitor.

A better solution than solder plating the region of the lead frame thatwill be joined to the negative terminal of the capacitor element is toselectively coat this surface with a protective, conductive coating thatcannot melt at reflow temperatures and is not likely to oxidize orcorrode. Suitable coatings include palladium, platinum, and gold. Thus,the metallic terminal has a protective coating on at least the surfaceconnected to the metal-powder-filled paint layer. The protective coatingmay also be plated on the surface external to a protective conformalcase of the finished capacitor. The protective coating may cover theentire surface of the metallic terminal. The protective coatings promotelow-resistance connections to the capacitor element(s) and to theexternal circuit.

A suitable metallic terminal is fabricated from alloy 194, which is analloy made predominantly from copper, giving it much higher electricalconductivity than other, more conventionally used alloys. The alloy 194terminal metal is either selectively plated with palladium (or gold)only in the region to be joined to the negative terminal of thecapacitor element, or palladium (or gold) plated overall. The terminalmetal is then selectively solder plated, but generally only in theregions that will be exterior to the protective case of the finishedcapacitor. The positive terminal(s) of the capacitor element(s) areresistance welded to the alloy 194 lead frame. Successful welding occursbecause the welding electrodes are chosen to be a high-melting-pointmaterial which has acceptable conductivity, optimal welding parametersare employed, and the weld is generated at the optimal location on thelead frame metal. An example of a conventional metallic terminal is onefabricated from solder-plated alloy 752 which has approximately tentimes the electrical resistivity of alloy 194, but which can be reliablywelded using conventional electrodes and welding schedules.

Preferably the electrodes of the resistance welder are made from ahigh-melting point material (e.g., anviloy) that does not readily stickto either the metallic terminal or the positive terminal(s) of thecapacitor element(s) during the welding schedule. Further the weldingschedule is modified to increase the current during welding, but shortenthe welding time versus welding schedules commonly used with moreconventional metallic leadframe alloys. This modified welding scheduleimproves weld integrity by accommodating the high-conductivity leadframemetal's tendency to rapidly heat sink and dissipate welding heat bygenerating this heat in a shorter time frame before it can bedissipated. Preferably the weld(s) is/are formed at the extreme edge ofthe leadframe to further limit the loss of welding heat during the weldschedule due to the high thermal conductivity of metals that have highelectrical conductivity.

EXAMPLES Example 1

Multi-element MnO₂-impregnated, tantalum-oxide, surface mount capacitorswere fabricated similar to those described by Piper (U.S. Pat. No.3,686,535, see FIG. 1). Six identical tantalum capacitor elements werefabricated in accordance with the invention and connected electricallyin parallel as shown in FIG. 2. The median ESR performance of thesecapacitors demonstrates the efficacy of the capacitors of the invention.The capacitor elements were connected to the external circuit by meansof thin metallic strips (originally part of a larger lead framestructure) to which the positive terminals of the capacitor elementswere welded and to which the negative terminals of the capacitorelements were electrically connected by means of conductive silveradhesive.

Individual tantalum capacitor elements were fabricated by pressingtantalum flake or powder into a compacted rectangular slug at 25% to 75%theoretical density. A tantalum wire exited one narrow surface of theslug (or was welded to the surface of the slug) and ultimately becamethe positive terminal of the capacitor element. This slug was sinteredat high temperature to fuse the individual tantalum particles togetherwhile maintaining maximum practical porosity and internal surface area.

Tantalum oxide was grown electrolytically on the surface of the poroustantalum slug and resulted in partial consumption of the underlyingtantalum metal. The tantalum oxide behaves as the dielectric of thefinished capacitor. Electrical connections were made to the exposedsurface of the dielectric before the capacitor element could beelectrically connected to an external circuit.

The electrical connection to the exposed surface of the dielectric wasfabricated in layers, and the layers were applied in a specific order sothat only compatible materials were in contact with each other,specifically, placed in order on the tantalum-oxide dielectric weremanganese dioxide (MnO₂) or conductive polymer, graphitic carbon, andmetal paint. The metal paint was the external surface and negativeterminal of the finished capacitor element and was then attached to thenegative terminal of the finished, 6-element capacitor by means ofconductive, metal-filled epoxy adhesive.

Capacitors were constructed per the method described above using eightdifferent combinations of materials. The materials included graphiticcarbon, silver paint, and metallic terminals within and outside thescope of the invention. Groups of capacitors, representative of each ofthe eight material combinations, were measured to determine the medianESR of that combination of materials. Then the devices were exposed tovarious cumulative environmental stresses with measurements made aftereach stress.

Trials to Establish the Efficacy of the Various Combinations

The materials within the scope of the invention were compared toconventional materials. All eight possible combinations of materialswere tested to identify unexpected interactions among the variousmaterials. The results are presented as the median ESR value perexperimental group. The median ESR value is the ESR value that is bothhigher than that of half the group's members and lower than that of theother half of the group's population.

The performance of each test group was evaluated (measured)“as-manufactured” and after several cumulative exposures to severeenvironmental stress. The environmental stresses were 3 passes through astandard IR reflow process with peak temperature of 235° C., 134 hoursof exposure to 85% relative humidity at 121° C. (called “HAST” testing),500 cycles of thermal shock between −55° C. and +125° C., 1000 hours oflife test exposure at 150° C. biased with 0.5 times rated voltage, and1000 hours of life test exposure at 175° C. biased with 0.5 times ratedvoltage. Each of these stresses exceeded the normally expectedenvironmental exposure during a capacitor's life, but the severity ofthe exposures helps to highlight the strengths and weaknesses of variousmaterial combinations.

Table 1 contains median ESR values in units of milliohms. For each ofthe three kinds of material (carbon, metal paint, and metallicterminals), one material is conventional while the other material iswithin the scope of the invention. Data is provided for the devices“as-manufactured” and after each of the cumulative environmentalstresses.

TABLE 1 ESR (mΩ) 2001 M, DP5262, 2001 M, DAG DP5262, DAG Alloy JM-P59001050 JM-P5900 1050 As Mfg 752 10.4 10.0 9.2 8.7 As Mfg 194 7.7 7.5 6.86.6 Post 3 IR 752 12.8 13.3 9.9 8.8 Reflows Post 3 IR 194 11.6 9.4 6.96.4 Reflows Post 134 hr 752 18.4 20.0 12.0 9.0 unbiased HAST Post 134 hr194 16.1 12.8 9.0 6.7 unbiased HAST Post 500 Cycles 752 16.1 15.3 11.99.6 Thermal Shock Post 500 Cycles 194 13.0 10.3 8.7 6.9 Thermal ShockPost 1000 hr, 752 15.4 14.2 11.4 10.3 150C Life Post 1000 hr, 194 11.69.2 8.0 7.0 150C Life Post 1000 hr, 752 40.6 14.6 33.6 12.1 175C LifePost 1000 hr, 194 36.8 9.9 26.7 8.2 175C Life

Table 2 contains ESR-difference data which show the relative benefit ofthe graphitic carbon within the scope of the invention versusconventional graphitic carbon, not only “as-manufactured,” but alsoafter each of the cumulative environmental shifts. Positive numbersindicate that the inventive graphitic carbon indeed produced superiorperformance; negative numbers indicate that the inventive materialproduced inferior results. The right-most column of data contains theaverage improvement generated in all of the test cells by choosing theinventive graphitic carbon. This column provides two kinds ofinformation: (1) the “as-manufactured” advantage of using the inventivemicrographited carbon suspension, and (2) which type of environmentalstress truly highlights the superiority of the inventive micrographitedcarbon suspension.

TABLE 2 Difference in 100 kHz ESR (mΩ) due to JM-P5900 vs. DAG 1050Carbon Silver Paint: 2001M 2001M DP5262 DP5262 Avg Shift Leadframe:Alloy 752 Alloy 194 Alloy 752 Alloy 194 due to C As Mfg 0.4 0.2 0.5 0.20.3 post 3 IR −0.5 2.2 1.1 0.5 0.8 reflows post 134 hr −1.6 3.3 3.0 2.31.8 unbiased HAST post 500 0.8 2.7 2.3 1.8 1.9 Cycles Thermal Shock post1000 hr 1.2 2.4 1.1 1.0 1.4 150C Life post 1000 hr 24.0 26.9 21.5 18.522.7 175C Life

Table 3 contains ESR-difference data which show the relative benefit ofthe silver paint within the scope of the invention versus conventionalsilver paint, not only “as-manufactured,” but also after each of thecumulative environmental shifts. Positive numbers indicate that theinventive silver paint indeed produced superior performance; negativenumbers indicate that the inventive material produced inferior results.The right-most column of data contains the average improvement generatedin all of the test cells by choosing the superior silver paint. Thiscolumn provides two kinds of information: (1) the “as-manufactured”advantage of using the inventive metal paint, and (2) which type ofenvironmental stress truly highlights the superiority of the inventivemetal paint.

TABLE 3 Difference in 100 kHz ESR (mΩ) due to 2001M vs. DP5262 SilverPaint Carbon: JM-P5900 JM-P5900 DAG1050 DAG1050 Avg Shift Leadframe:Alloy 752 Alloy 194 Alloy 752 Alloy 194 due to Ag As Mfg 1.2 0.9 1.3 0.91.1 post 3 IR 2.9 4.7 4.5 3.0 3.8 reflows post 134 hr 6.4 7.1 11.0 6.17.7 unbiased HAST post 500 4.2 4.3 5.7 3.4 4.4 Cycles Thermal Shock post1000 hr 4.0 3.6 3.9 2.2 3.4 150C Life post 1000 hr 7.0 10.1 2.5 1.7 5.3175C Life

Table 4 contains ESR-difference data which show the relative benefit ofthe metallic lead frame within the scope of the invention versus aconventional metallic lead frame, not only “as-manufactured,” but alsoafter each of the cumulative environmental shifts. Positive numbersindicate that the inventive material indeed produced superiorperformance; negative numbers indicate that the inventive materialproduced inferior results. The right-most column of data contains theaverage improvement generated in all of the test cells by choosing theinventive metallic lead frame. This column provides two kinds ofinformation: (1) the “as-manufactured” advantage of using the inventivemetallic terminal alloy, and (2) which type of environmental stresstruly highlights the superiority of the inventive metallic terminalalloy.

TABLE 4 Difference in 100 kHz ESR (mΩ) due to Alloy 752 vs. Alloy 194Leadframe Avg Shift Carbon: JM-P5900 JM-P5900 DAG1050 DAG1050 due toSilver Paint: 2001M DP5262 2001M DP5262 leadframe As Mfg 2.7 2.4 2.5 2.12.4 post 3 IR 1.2 3.0 3.9 2.4 2.6 reflows post 134 hr 2.3 3.0 7.2 2.33.7 unbiased HAST post 500 3.1 3.2 8.0 2.7 4.3 Cycles Thermal Shock post1000 hr 3.8 3.4 5.0 3.3 3.9 150C Life post 1000 hr 3.8 6.9 4.7 3.9 4.8175C Life

Analysis of Experimental Test Data

The “as-manufactured” section of Table 1 demonstrates that thecombination of all inventive materials does indeed, produce superiorresults. That is, the combination of DAG1050 graphitic carbon, DP5262silver paint, and selectively plated alloy 194 metallic lead frame(second line of far-right column in the “as-manufactured” section)produced the lowest median ESR (6.6 mΩ) of any of the competingcombinations. However many of the other combinations of inventive andconventional materials produced very low ESR.

Table 1 also contains median ESR data for each competing combination ofmaterials after the devices are cumulatively exposed to a variety ofenvironmental stresses. Review of the data in the post-environmentalstress sections of Table 1 reveals that the combination of inventivematerials continues to have the best performance after each cumulativeenvironmental stress. The superiority of the invention is the mostpronounced after 134 hours of HAST humidity testing and after 1000 hoursat 175° C. However many of the other combinations of inventive andconventional materials produced substantially stable ESR in the face ofsevere environmental stress.

Finally, after each cumulative exposure to environmental stress, the ESRof capacitors manufactured with the combination of only inventivematerials (the optimal combination of the present invention) remainssubstantially stable while significant (and, sometimes, dramatic) ESRincreases are observed for many of the other combinations of materials.The performance gap between the combination of all inventive materialsand the other combinations grew as the devices received additionalenvironmental stress.

At the end of testing, the spread of performance among the combinationsof material had widened by an amount that was unanticipated, and couldnot have easily been predicted based on the “as-manufactured”performance of the combination of inventive materials. This points to asynergistic response among the inventive materials when they are used incombination and are then exposed to severe environmental stress.However, several of the combinations of inventive and conventionalmaterials also produced ESR stability that can only be explained bysynergism among the inventive materials.

In Tables 2 through 4, the benefit of each kind of superior material isanalyzed, one material per table. The impact of the superior graphiticcarbon is revealed in Table 2, the impact of the superior silver paintis revealed in Table 3, and the impact of the superior metallic leadframe is revealed in Table 4.

In the “as-manufactured” row of Table 2, the overall benefit derivedfrom using the inventive graphitic carbon (DAG1050) with allcombinations of silver paint and metallic lead frame is a 0.3 mΩreduction in ESR. The overall benefit of the inventive graphitic carbonbecomes more pronounced after cumulative environmental stress, where themost significant results are seen after 1000 hours at 175° C. Thisindicates that the greatest contribution provided by the inventivegraphitic carbon is stability after lengthy exposure to very hightemperatures. After 1000 hours at 175° C., the smallest overall shitoccurs in the table column that contains data for the combination of theinventive silver paint (DP5262) and the inventive metallic lead frame(Alloy 194), demonstrating the synergistic effect of these two superiormaterials when exposed to elevated temperatures for long periods.

Interestingly enough, using the inventive graphitic carbon (instead ofthe conventional JM graphitic carbon) along with the combination ofconventional silver paint (2001M) and conventional lead frame (Alloy752) actually results in a small deterioration of ESR performance afterIR reflow and HAST exposure. Thus the results obtained with all threeinventive materials in combination was not expected.

In the “as-manufactured” row of Table 3, the overall benefit derivedfrom using the inventive silver paint (DP5262) with all combinations ofgraphitic carbon and metallic lead frame is a 1.1 mΩ reduction in ESR.The overall benefit of the inventive silver paint becomes morepronounced after cumulative environmental stress, where the mostsignificant results are seen after 134 hours of HAST testing. Thisindicates that the greatest contribution provided by the inventivesilver paint is stability after exposure to intense moisture. Theinventive silver paint also makes a significant contribution to ESRstability after 1000 hours at 175° C. After both 134 hours of HASTtesting and 1000 hours at 175° C., the smallest overall shifts occur inthe table column that contains data for the combination of the inventivegraphitic carbon (DAG1050) and the inventive metallic lead frame (Alloy194), demonstrating the synergistic effect of these two inventivematerials when exposed to intense moisture and elevated temperatures forextended periods.

In the “as-manufactured” row of Table 4, the overall benefit derivedfrom using the inventive metallic lead frame (Alloy 194) with allcombinations of graphitic carbon and silver paint is a 2.4 mΩ reductionin ESR. The overall benefit of the inventive metallic lead frame becomesmore pronounced after cumulative environmental stress, where the mostsignificant results are seen after 500 cycles of thermal shock and after1000 hours at 175° C. This indicates that the greatest contributionprovided by the inventive metallic lead frame is stability after rapidtemperature changes and stability after lengthy exposure to very hightemperatures. After thermal shock and 1000 hours at 175° C., thesmallest overall shifts occur in the table column that contains data forthe combination of the inventive graphitic carbon (DAG1050) and theinventive silver paint (DP5262), demonstrating the synergistic effect ofthese two superior materials when exposed to thermal shock and elevatedtemperatures for long periods.

Overall, the experimental data demonstrate that the best (lowest) ESRperformance is achieved when all three inventive materials (andassociated methods) are used in combination (the optimal combination ofthe invention). Also, the data demonstrate that the capacitorsmanufactured from the inventive materials are remarkably more stablethan capacitors manufactured from more conventional materials when thecapacitors are exposed to severe environmental stress. This unexpectedlybetter stability demonstrates a synergistic relation among the superiormaterials when they are used in combination and are then exposed toenvironmental stress.

Detailed analysis of the data, material by material, not onlydemonstrates the benefit of each inventive material in capacitors“as-manufactured,” but also demonstrates how this benefit is magnifiedby exposure to severe environmental stress. These detailed analysesprovide insight into which inventive material provides significantrobustness to one or more specific environmental stresses, and alsodemonstrate lower-level synergies among the inventive materials whenthese materials are taken two at a time.

The degree of ESR stability observed in capacitors constructed from allthree of the inventive materials was wholly unanticipated and could nothave been predicted based on the “as-manufactured” ESR performanceobserved for this combination of materials. This unanticipated stabilitydemonstrates a synergy among the inventive materials that was hithertounknown and could not be predicted. The lowest and most stable ESR isobtained when all three of the inventive materials are usedsimultaneously. However, measurable improvements in ESR and ESRstability can be obtained by using the inventive materials either two ata time or one at a time, in combination with conventional materials andmethods.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the compositions and methodsof the present invention without departing from the spirit or scope ofthe invention. Thus, it is intended that the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

What is claimed is:
 1. A valve metal capacitor comprising at least oneanodized element having a dielectric layer formed on the element, aconductive layer formed on the dielectric layer, a graphitic carbonlayer formed on the conductive layer, a metal-powder-filled paint layerformed on the graphitic carbon layer, and a negative metallic terminalattached to the paint layer; wherein at least one of 1) the graphiticcarbon layer is formed from graphitic carbon having at least 73%graphite carbon in a binder stable at temperatures of at least 150° C.or a binder that decomposes into conducting species when exposed toreflow temperatures; 2) the metal-powder-filled paint layer has aresistivity of less than about 0.0005 Ω·cm and comprises metal powder ina binder stable at temperatures of at least 200° C.; or 3) the negativemetallic terminal has a conductivity of at least 90% the conductivity ofpure copper, wherein at least the surface of the negative metallicterminal connected to the metal-powder-filled paint layer is plated witha protective coating to prevent oxidation of the negative metallicterminal, and wherein the protective coating is thermally stable attemperatures of at least 200° C.
 2. The capacitor according to claim 1wherein the valve metal is tantalum, aluminum, niobium, titanium, ormixtures, alloys, or metallic glasses thereof.
 3. The capacitoraccording to claim 1 wherein the conductive layer formed on thedielectric layer is manganese dioxide, a conductive polymer, or aconductive salt.
 4. The capacitor according to claim 1 wherein thethickness of the carbon layer is between about 0.0001 inches to about0.003 inches.
 5. The capacitor according to claim 1 wherein paint layercontains more than 80% metal content by weight after drying.
 6. Thecapacitor according to claim 1 wherein the metal powder in the paint issilver, gold, nickel, copper, mixtures, or alloys thereof.
 7. Thecapacitor according to claim 6 wherein the metal powder in the paint issilver.
 8. The capacitor of claim 1 wherein the binder in the paintcomprises a thermosetting epoxy, a thermosetting polyimide, or asilicone epoxy which does not melt or outgas at temperatures of at least200° C.
 9. The capacitor of claim 1 wherein the binder in the paint issubstantially free from mobile ionic species after curing to minimizeoxidation or corrosion when the cured paint is exposed to moisture. 10.The capacitor according to claim 1 wherein the negative metallicterminal is pure copper, silver, or an alloy having at least 90%conductivity of copper.
 11. The capacitor according to claim 10 whereinthe negative metallic terminal is pure copper.
 12. The capacitoraccording to claim 1 wherein the protective coating is palladium,platinum, or gold.
 13. The capacitor of claim 1 wherein the protectivecoating is further plated on the surface external to a protectiveconformal case of the finished capacitor.
 14. The capacitor of claim 1further comprising at least one positive metallic terminal connected toan anode lead wire embedded in the element wherein the positive metallicterminal has a conductivity of at least 90% the conductivity of purecopper.
 15. The capacitor of claim 14 wherein the positive metallicterminal is joined to the anode lead by resistance welding, laserwelding, or ultrasonic welding.
 16. The capacitor of claim 1 wherein thenegative metallic terminal comprises an endcap which covers the negativeend of the element.
 17. The capacitor of claim 16 further comprising apositive metallic terminal comprising an endcap which covers thepositive end of the element.
 18. The capacitor of claim 17 wherein theconnection to the negative metallic terminal comprises a conductivemetal-filled adhesive, and the connection to the positive metallicterminal comprises a weld.
 19. The capacitor of claim 1 wherein theprotective coating covers the whole region of the negative metallicterminal that will be encapsulated by a protective conformal case. 20.The capacitor of claim 1 wherein the protective coating further coversthe whole region of the positive metallic terminal that will beencapsulated by a protective conformal case.
 21. The capacitor of claim1 wherein a solder plating is plated on the surface of the negativemetallic terminal external to a protective conformal case of thefinished capacitor.
 22. The capacitor of claim 21 wherein the solderplating is tin or a tin-lead mixture.
 23. The capacitor of claim 14wherein a solder plating is plated on the surface of the positivemetallic terminal external to a protective conformal case of thefinished capacitor.
 24. The capacitor of claim 1 wherein the negativemetallic terminal is joined to the metal-powder-paint layer with asilver-filled conductive adhesive, a gold-filled conductive adhesive, ora nickel-filled conductive adhesive.
 25. A valve metal capacitorcomprising at least one anodized element having a dielectric layerformed on the element, a conductive layer formed on the dielectriclayer, a graphitic carbon layer formed on the conductive layer, ametal-powder-filled paint layer formed on the graphitic carbon layer,and a negative metallic terminal attached to the paint layer; wherein atleast two of 1) the graphitic carbon layer is formed from graphiticcarbon having at least 73% graphite carbon in a binder stable attemperatures of at least 150° C. or a binder that decomposes intoconducting species when exposed to reflow temperatures; 2) themetal-powder-filled paint layer has a resistivity of less than about0.0005 Ω·cm and comprises metal powder in a binder stable attemperatures of at least 200° C.; or 3) the negative metallic terminalhas a conductivity of at least 90% the conductivity of pure copper,wherein the surface of the terminal is selectively plated with aprotective coating to prevent oxidation of the negative metallicterminal and wherein the protective coating is thermally stable attemperatures of at least 200° C.
 26. A valve metal capacitor comprisingat least one anodized element having a dielectric layer formed on theelement, a conductive layer formed on the dielectric layer, a graphiticcarbon layer formed on the conductive layer, a metal-powder-filled paintlayer formed on the graphitic carbon layer, and a negative metallicterminal attached to the paint layer; wherein 1) the graphitic carbonlayer is formed from graphitic carbon having at least 73% graphitecarbon in a binder stable at temperatures of at least 150° C. or abinder that decomposes into conducting species when exposed to reflowtemperatures; 2) the metal-powder-filled paint layer has a resistivityof less than about 0.0005 Ω·cm and comprises metal powder in a binderstable at temperatures of at least 200° C.; or 3) the negative metallicterminal has a conductivity of at least 90% the conductivity of purecopper, wherein the surface of the terminal is selectively plated with aprotective coating to prevent oxidation of the negative metallicterminal and wherein the protective coating is thermally stable attemperatures of at least 200° C.
 27. A multiple element capactorcomprising at least two capacitor elements wherein at least one of theelements is according to claim
 1. 28. The multiple element capactor ofclaim 27 further comprising at least one ceramic capacitor element. 29.The capacitor of claim 1 comprising more than one anodized element, eachelement having a set of positive and negative metallic terminals,wherein each set of metallic elements are collectively joined into aleadframe.